The present invention relates generally to methods and apparatus for braking vehicles and more especially to such methods and apparatus for the selective control of electrically actuated aircraft braking systems.
An illustrative electrically actuated aircraft braking system is shown in U.S. Pat. No. 4,865,162 which teaches a plurality of annularly disposed electrically energizable torque motor and roller screw drive mechanisms for selectively engaging a pressure plate of a wheel and brake assembly and compressing a disc brake stack to retard aircraft motion. In such electrically actuated braking systems, all electromechanical actuators associated with a given wheel are actuated each time the brakes for that wheel are applied. This can result in undesirable heating of the brake assembly and sometimes unnecessary wear of the brake disks. Moreover, failure of one or more electromechanical actuators can result in uneven braking and a tendency for the aircraft to xe2x80x9cpullxe2x80x9d away from the side on which the failure has occurred due to a now lesser braking force on that side. Finally, most braking systems sometimes experience a xe2x80x9cchatterxe2x80x9d or undesirable vibration during a braking event.
The problem of disk wear is addressed in U.S. Pat. No. 4,923,056 where it is suggested to energize less than all of the brake assemblies during braking associated with slower speed taxi or towed situations where lesser braking force is required. While this patented system may alleviate the disk wear problem, all electromechanical actuators associated with a given wheel are actuated each time the brakes for that wheel are applied leaving the problems of undesirable heating of the brake assembly, vibration and uneven braking unresolved.
It is desirable to provide a braking system which reduces brake induced vibration, undesired unbalanced braking force, and unnecessary brake assembly heating all at a very modest increase in braking system cost.
The present invention provides solutions to the above problems by providing individual electromechanical actuator control within a brake system. Active vibration damping is a benefit of this system design and architecture, as are enhanced fault accommodation, improved thermal management and improved park and tow capabilities.
In accordance with one form of the invention, a braking system of the type having a plurality of individual actuators selectively energizable upon a braking command to frictionally restrain rotation of a vehicle wheel includes a control circuit operable in a normal braking mode to equally or unequally energize all of the plurality of actuators upon receipt of a braking command, and in a second mode to equally or unequally energize less than all of the plurality of actuators associated with a given wheel upon receipt of a braking command. The second mode may be a taxi mode where less than all actuators (a proper subset of all actuators for that brake) are enabled to diminish heat generation and energy consumption, a mode where the actuators are enabled in a routine to reduce brake vibration, or a failed actuator mode where a failed actuator and a matching actuator on the opposite side of the vehicle are disabled to maintain equal left-right retarding forces on the vehicle. An alternative failed actuator mode involves increasing the level of energization to the remaining actuators associated with the wheel of the failed actuator.